Thread: Where do you put the catch can?

Originally Posted by AndrewMilne

I have some questions about this, and Davetd5's post (which prompted Muppet's reply):
When the turbo charger is working a lot, won't it blow condensed oil from inside the intercooler into the inlet manifold and then the cylinders, where it gets burnt?
If not, and oil still accumulates, why is there not a drain plug (or a pipe/hose with a drain-tap on the end) in the bottom of the intercooler?
If you are going to remove an intercooler for cleaning, wouldn't fitting such a drain to the bottom of it eliminate the need for a catch-can?
Has anyone tried this and, if so, with what result?

The oil condenses in the inter-cooler. The oil is fairly thick and will flow slowly out, I think you would need to have the inter-cooler passages sloping left or right to assist drainage. I just think that the viscosity of the oil will be too much of a hindrance.

Agreed.
The provent is a far simpler solution.

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I installed a catch can on my TDI Discovery and managed to fit it next to the second battery. I inserted the breather from the catch can into a hole in the chassis out the way. Tight fit lovely job, what wasn't so lovely was the the back pressure was to high caused by the catch can , resulting in oil being pushed out through the gaskets in the engine. I disconnected it real quick, the catch can is still sitting in place. May be the outlet should go back to the air inlet? But it seems a waste of time generally.


Landy Adrian

Originally Posted by landyadrian

I installed a catch can on my TDI Discovery and managed to fit it next to the second battery.
Landy Adrian

Can you post a photo or two? I have the rack for a second battery.

You won't get back pressure if catch can is connected to the air inlet.

The Issue with the intercooler is that the entire inside gets coated with oil which reduces the conductivity of the aluminium, so reduces its efficiency.
When I removed mine at 135KK there was no oil to run out of it.

You have to slosh turps/petrol or similar around inside to remove the oil from the tubes. I then dried mine with a vacuum cleaner on blow.

The rocker cover only vents to the inlet manifold when the vacuum is low,ie when you have your foot lightly on the accelerator . The valve on top closes at other times. So maybe replacing the valve could be positive . If I were to fit a catch can , I would plumb the outlet back to the valve, so that any mist was caught in the can, but the original design was maintained.

Regards Philip A

Originally Posted by landyadrian

I installed a catch can on my TDI Discovery and managed to fit it next to the second battery. I inserted the breather from the catch can into a hole in the chassis out the way. Tight fit lovely job, what wasn't so lovely was the the back pressure was to high caused by the catch can , resulting in oil being pushed out through the gaskets in the engine. I disconnected it real quick, the catch can is still sitting in place. May be the outlet should go back to the air inlet? But it seems a waste of time generally.


Landy Adrian

So incorrectly sized for the task then

Originally Posted by PhilipA

The Issue with the intercooler is that the entire inside gets coated with oil which reduces the conductivity of the aluminium, so reduces its efficiency.
When I removed mine at 135KK there was no oil to run out of it.

You have to slosh turps/petrol or similar around inside to remove the oil from the tubes. I then dried mine with a vacuum cleaner on blow.

The rocker cover only vents to the inlet manifold when the vacuum is low,ie when you have your foot lightly on the accelerator . The valve on top closes at other times. So maybe replacing the valve could be positive . If I were to fit a catch can , I would plumb the outlet back to the valve, so that any mist was caught in the can, but the original design was maintained.

Regards Philip A

Hi Philip,
Thank you for that post, which is informative and makes sense.
From what you say, it seems that the downside of having oil in the intercooler is essentially that air compressed & heated by the turbo will not be cooled as much as it would otherwise be, before entering the engine.
Not that the airflow through the intercooler is significantly reduced (if there is not enough oil present in the intercooler to pool or flow out).

Under normal operation, you say the rocker cover vents to the inlet manifold only at low throttle.
But under acceleration, when the turbo is working, isn't it effectively doing the same, only via the intercooler?
Or does ALL / MOST of the oil in the ventilation flow get caught in the intercooler?

I may have missed something here, but wouldn't simply routing the crank-case ventilation directly to the inlet manifold under all circumstances be much the same (and eliminate the oil-in-the-intercooler problem)?

Regards, Andrew

Originally Posted by AndrewMilne

Hi Philip,
Thank you for that post, which is informative and makes sense.
From what you say, it seems that the downside of having oil in the intercooler is essentially that air compressed & heated by the turbo will not be cooled as much as it would otherwise be, before entering the engine.
Not that the airflow through the intercooler is significantly reduced (if there is not enough oil present in the intercooler to pool or flow out).

Under normal operation, you say the rocker cover vents to the inlet manifold only at low throttle.
But under acceleration, when the turbo is working, isn't it effectively doing the same, only via the intercooler?
Or does ALL / MOST of the oil in the ventilation flow get caught in the intercooler?

I may have missed something here, but wouldn't simply routing the crank-case ventilation directly to the inlet manifold under all circumstances be much the same (and eliminate the oil-in-the-intercooler problem)?

Regards, Andrew

If you were to vent crank case to inlet manifold the result wouldn't be pretty as you would be feeding boost pressure in to crankcase. The very least would blow every oil seal in the engine , worst case would be very bad .
Philips analogy is more indicative of naturally aspirated petrol,I'm sure he didn't mean to say inlet manifold . Intercooler observation spot on , as are most of his posts. The valve on a td5 will open when pressure in the crankcase is positive and yep that's usually at idle / no load situations , unless you have excessive blow by due to worn compression rings